Combined voltage and current transformer



y 1953 A. MEYERHANS El AL 2,637,821

COMBINED VOLTAGE CURRENT TRANSFORMER Filed Sept. 15, 1950 2 SI-IEETSSI-IEET 1 3nventor 3'.

Gttomegs.

y 5', 1953 A. MEYERHANS ET AL 2,637,821

COMBINED VOLTAGE AND CURRENT TRANSFORMER Filed Sept. 13, 1950 2 SHEETS-SHEET 2 Zmnentors Gttornegs.

Patented May 5, 1953 UNITED STATES PATENT OFFICE COMBINED voL'rAoa-ANn .ouaaENr TRANSFORMER August Meyerhans, 'Nussbaumen, near- Baden, and Hans Hartmann, Baden, switzerlanmi'as signers to ,Aktiengesellschatt :Brown; .Boyeri .&

'Cie., Baden, Switzerland:

Application September '13, 1950, Serial No. 184,622' InSw'itzerland August-=4; 1949' The combination of voltage and current transformers in a single unit is a very desirable object in connection with the design of hi h. voltage measuring apparatus, because such ,a.

combination has a. favourable effect onthe price and requires very little space when it has to be installed in an electric plant.

It has-already been proposed to combinecur rent and voltage transformers to such an extent that both systems are linked together. The flux-conducting; parts of the voltage transformer have for instance been located parallel to the high voltage winding of the current transformer. Combined arrangements with electromagnetic interlinkage of those parts of the current and voltage transformers which form the flux and current circuits, require the provision of additional means, such as for instance special. separating slots in order to avoid short circuits between windings. This can however have a detrimental efiTect on the measuring accuracy. Attempts have also been made to construct such combined transformers for instance by employing open iron cores, but this also has an undesirable effect" on the measuring qualities.

ihe object cfthe present invention is to combine two transformers, each of which has most favourable measuring and constructional prop erties, so as to form .a single unit. As regards the voltage transformer, the most favourable properties .are achieved with two wound limbs and a closed magnetic circuit. It is then also possible to provide means which allow the potential to increase uniformly from the earthed end of the winding to the high-voltage end. The current transformer is preferably constructed with a ring winding, because as regards current strength this enables a most universal type to be obtained whilst retaining maximum measuring properties. Its high voltage winding is expediently constructed as a circular winding with straight leading-in wires, and both parts are surrounded with a jointless insulating casing, for instance of paper. The annular part of the insulating casing is preferably covered with an earthed conductive layer.

The present invention thus concerns the combination of a. voltage transformer with a current transformer of the same phase, consisting of a electromagnetically Voltage transformer with two-limhed magnetic circuit and with anapproximately uniformly increasing-potential from earth up .tothe. high volt.,-.

ageside, and furthermore a current transformer with a ring-shaped high-voltage winding erabedded in an i-nsulatii'lg casing and straight insulatedleadingdn wires, the limbs of theyol-te.

age transformer and the leads of the current. transformer being housed within an insulating covering.

A. constructional example of the invention is illustrated in the accompanying data-wing in schematicmanner, whereFig. '11 shows a come bined voltage and current. .tra -.sformer partly elevation .andpar-tly. in vertical section, Fig. 2a-

cross-section of thesame combined unit, and. 3 .is a; fragmentary perspective view, enlarged The high-voltag win-ding of the volta e transformer :is, indicated by-c. .An insulating cy-line den d made-of paper layers is provided between the hishandlow-uoltage winding-send insulatingwashersd' arearraneed between sections-of.

the. high-voltage, winding 01' which consists of a number of insulatedpart coils, each coil onone limb alternately connected to they next coil-.orzntheother limb-as shown schematically in r Fig. The

coilconnections-are indicated'in Figs. 2 3.]oy, reference letter c. By this means a potential gradient is achieved which increases approxie matel-y uniformly from earth to the -high-yoltageside. The high-voltage winding J of the current transformer is ring shaped and within a hollow metal annulus n which has an opening defined by a flaring upper wall section which merges smoothly into a metal tube 0. The current connections to the ring winding are established by the straight leads g1, 92 which pass through the tube 0 and are insulated from the tube and from each other by a plurality of washers w of insulating material and having slots through which the leads are threaded. The annular housing n and the metal tube o are enclosed within insulating paper windings In, in respectively, and care should be taken that the transition from one winding to the other is effected smoothly and that there are no discontinuities or air spaces where the paper windings merge into each other.

Reference letters i1, i2 indicate the iron cores which support the low-voltage winding of the current transformer and surround the insulated ring-shaped high-voltage winding j. Both wound limbs of the voltage transformer and the insulated leads of the current transformer are arranged inside the insulator m in such a manner that when regarded in plan view they form the corners of an approximately equilateral triangle. The uniformly rising potential of the voltage transformer is utilized to control the voltage gradient along the insulationhz of the leads of the current transformer. This is for instance achieved by means of insulated control rings 1' which are arranged on the insulating sneath 17.2 of the current transformer leads and are connected to the coils of the voltage transformer. Both limbs of the voltage transformer and the leads of the current transformer can be arranged in parallel planes, as shown in the drawing, or inclined towards each other. surface of the insulation winding hz not covered by the control rings r, and the outer insulating winding hi, are provided with a. metallized coating is.

The arrangement according to the invention has the advantage that the ceramic insulator m which is used for enclosing at least the active parts of the transformer combination and also serves as an oil container, has the smallest possible diameter. This is important because the ceramic insulator is practically the most expensive element of the combined unit. When compared with the diameter of the ceramic insulator required for a simple voltage transformer, the diameter of the insulator used for a combined transformer unit in accordance with the invention is only slightly larger, because the leads trolling elements 1' on the insulation winding 712 f of the current transformer leads are therefore utilized to improve the voltage distribution when a voltage impulse occurs, the control rings on the current transformer being used to produce a capacitive effect on the part coils of the highvoltage Winding of the voltage transformer. The 5 currents flowing from the high-voltage windingto the low-voltage winding of the voltage transformer are thus entirely or partly supplied by The outer I the high-voltage Winding of the current transformer. The result is that the voltage distribution along the voltage transformer is approximately linear.

We claim:

1. The combination of a voltage transformer with a current transformer of the same phase, said combination comprising a voltage transformer with a two-limbed magnetic circuit, a high voltage primary Winding including a plurality of individual coils on each limb of the magnetic circuit and serially connected in alternation from the grounded end to the high voltage end of said winding, thereby to provide an approximately uniformly increasing potential distribution from the grounded end to the high voltage end of said winding, and a low voltage secondary winding including sections upon each of said limbs; and a current transformer having an annular high-voltage winding in an insulating casing and having straight, insulated leads, and an annular iron core threaded through said annular high voltage winding and carrying a secondary winding; the limbs of said voltage transformer and the leads of said current transformer being housed within an insulator.

2. Combination as in claim 1, characterised in that both limbs of the voltage transformer and the leads of the current transformer are so arranged in the insulator that they are located at the corners of an equilateral triangle.

3. Combination as in claim 2, characterised in that the limbs of the voltage transformer and the leads of the current transformer are located in parallel planes.

4. Combination as in claim 1, in combination with an insulating sheath through which said straight insulated leads extend, and means energized by voltage transformer to establish a voltage gradient along said sheath.

5. Combination as in claim 4, characterised in that said means comprises mutually insulated rings arranged on the insulating sheath of the current transformer leads and connected to the coils of the Voltage transformer in succession at spaced points along the same.

AUGUST MEYERI-IANS. HANS I -IARTMANN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,586,533 Peterson June 1, 1926 2,182,641 Poleck Dec. 5, 1939 2,314,851 Barney Mar. 23, 1943 2,431,244 Griscom Nov. 18, 1947 

